The present invention relates to a spray gun for atomizing fluid media with the help of compressed air, principally consisting of a housing with a handle and an atomizer nozzle which can be connected to a compressed air line, of a guide sleeve supported in the housing equipped with a feed line for the medium to be atomized, with one end of the guide sleeve engaging in the atomizer nozzle, as well as of a valve needle which can be operated against the force of a return spring in order to open the atomizer nozzle by means of a trigger handle which is in a pivoting mounting on the housing.
There are numerous different embodiments of spray guns of prior art which have also proven themselves to be effective in practice. In such embodiments, the valve needle projects out of the guide sleeve on the side facing away from the atomizer nozzle and also out of the housing of the spray gun, while a trigger handle in a pivoting mounting on the housing acts on the spray gun. The valve needle has a special seal in the guide sleeve to prevent the medium to be applied from leaking out of the interior of the guide sleeve. This is achieved in that a deformable seal is clamped in between the valve needle and the guide sleeve by means of a further sleeve which can be screwed into the guide sleeve.
Assembling the valve needle in the guide sleeve is difficult and time-consuming, since the clamping force which acts on the seal must be set exactly. This is because, if the preload on the seal is too great, the valve needle can only be moved by applying considerable force to it, while on the other hand if the preload is insufficient then there is a significant risk that medium will leak out during operation through the two ring gaps which are to be sealed. The stuffing gland arranged in the guide sleeve therefore represents a degree of uncertainty as far as achieving a correct seal is concerned. Furthermore, the seal is a considerable cost factor, since the stuffing gland is assembled from several interacting components which are subject to wear and also have to be replaced from time to time.
The purpose of the present invention is therefore to create a spray gun of the aforementioned type in such a way that straightforward assembly of the valve needle is possible within a short period of time and that a reliable means is provided to prevent the medium leaking out from the interior of the guide sleeve. The construction complexity by which this is to be achieved should be kept at a low level, therefore permitting economical manufacture and assembly of the spray gun. Also, the susceptibility to faults should be reduced over a long service life.
In the present invention, this is achieved in a spray gun in accordance with the pre-characterizing clause of claim 1 in that the valve needle is located in a positive connection with the trigger handle in the area of the guide sleeve by means of a hinge pin which passes through the valve needle and the guide sleeve and that a seal is inserted in the guide sleeve with a U-shaped cross section, the seal being located between the feed line and the hinge pin, with the valve needle being held in a movable arrangement in the seal.
It is advantageous in this arrangement for the valve needle to be provided with a thickened portion in the area of a bore which accommodates the hinge pin, with the thickened portion being adapted to the internal jacket surface of the guide sleeve, and for the valve needle to be provided with a collar in the end area facing away from the atomizer nozzle, serving as a stop for the return spring which is inserted in between the collar and a base of the guide sleeve.
The seal which accommodates the valve needle should be equipped with one or more lugs projecting along the length of the valve needle on one of its two sides, with each of the lugs having a slot and with projections formed on the valve needle engaging in the slots or between two lugs.
For the purpose of positionally-oriented assembly of the valve needle, it is furthermore advantageous for one or more, or in a preferred embodiment two, diametrically opposed contact surfaces to be formed onto the valve needle, in which case the contact surfaces should be worked into the valve needle between the tip of the valve needle and the seal which holds it.
The guide sleeve can be held in a partition wall of the housing in a straightforward way and be used to provide a seal in the atomizer nozzle with the help of a lip seal, as well as being supported axially on the partition wall of the housing by means of a stop surface.
Furthermore, it is advantageous for the valve needle to be made in one piece from plastic.
If a spray gun is configured in accordance with the present invention, then not only will reliable operation be assured at all times, but also the valve needle can be installed in the guide sleeve in a positionally-oriented manner without difficulty and excluding the possibility of the medium to be applied leaking out. This is because an assembly tool can be used to insert the valve needle together with the seal through which it is inserted and the return spring into the guide sleeve which is closed at one end, with the aforementioned components being inserted in such a way that the hinge pin by means of which the valve needle is held in a positive connection with the trigger handle can be installed without difficulty. There is no need to clamp special seals in this embodiment, and also only a few components are required to enable the stored medium to be applied in a metered fashion.
Economical production is possible since nearly all components, in particular also the single-piece valve needle, can be manufactured from plastic. Furthermore, the design ensures that malfunctions and wear to the few components which are to be moved during operation are practically excluded, so therefore the spray gun configured in accordance with the proposed invention can be guaranteed to achieve a lengthy service life.